There are a few variables on water pump and steam port pipe routing. I cut the factory hose nipple off of my steam port piping, drilled it out to 11/32 to the right depth, and threaded it for 1/8 npt. From there I used an 1/8 npt to 1/4 barb 90.
This thread has some good pictures as well, one of my favorite engine builds.
http://67-72chevytrucks.com/vboard/s...d.php?t=668385